Infection with hepatitis B virus (HBV) is a global public health problem, with a mortality rate that places it among the top 10 major infectious killers. The World Health Organization estimates that 400 million people are carriers of the virus worldwide. It has been estimated that acute HBV disease leads to 600,000 deaths annually; complications of chronic disease, including HBV-induced liver cirrhosis and hepatocellular carcinoma, account for about 400,000 deaths per year (El-Serag H B and Mason A C. N Engl J Med. 1999; 340 (10):745-750).
Many patients who are infected by the hepatitis B virus are unable to resolve the infection and develop chronic HBV, which may lead to deterioration of liver function, including cirrhosis and hepatic decompensation and a subsequent need for transplantation. Although the infected liver is removed before transplantation, some circulating virus still remains in the serum, and other reservoirs are believed to exist in other body compartments. Therefore, these patients are at high risk of HBV-reinfection of their transplanted liver.
Prevention of HBV infection may be achieved with active or passive immunization. Active immunization with recombinant HBV vaccines can prevent HBV infection if given before exposure. These vaccines, made from noninfectious viral subunits, have been shown to be safe and effective and confer long-term immunity.
Passive immunization with hepatitis B specific antibodies, given shortly after exposure, can decrease the incidence or severity of disease. Hepatitis B immune globulin (HBIG) is a plasma-derived, polyclonal preparation of antibodies to the hepatitis B surface antigen (anti-HBs). The antibodies bind to hepatitis surface antigen on the surface of the virus and neutralize it, thus preventing infection.
Passive immunization with HBIG is most effective if given when viral titers are low and an excess of antibody can be achieved. For this reason, HBIG has been effective in preventing new infections. It also appears to be partially effective when used to prevent reinfection after liver transplantation, where the viral load is decreased by removal of the infected organ. It has been especially effective in patients with low viral titers before surgery.
At present, there are three antiviral products available for treatment of chronic hepatitis B: interferon 2b (INTRON® A, Schering), lamivudine (EPIVIR HBV®, GlaxoSmithKline), and/or adefovir dipivoxil (HEPSERA™, Gilead Sciences). However, there is no therapy to cure chronic HBV infections in all patients. HBIG has not been effective in treating patients with chronic hepatitis B where persistent levels of virus are produced, and it is not possible to produce antibody excess without frequent administrations of antibody. End-stage liver disease related to chronic viral hepatitis is the leading indication for orthotopic liver transplantation (OLT) worldwide. The term “orthotopic” means that the diseased organ is removed and the new allograft is implanted in the normal or usual position in the right upper quadrant of the abdomen. OLT for cirrhosis and organ failure due to HBV infections accounts for 5% to 10% of all adult transplants. Protection of the transplanted liver from recurrent HBV infection is critical to preserving graft function. Life-long HBV prophylactic treatment is probably necessary, since virus remains in several other body compartments (spleen, lymph nodes, kidneys, skin, gastrointestinal tract, gonads, nerve ganglia, and brain) following removal of the infected liver. Hepatitis B infection of the liver reoccurs rapidly when the patient is immunosuppressed after transplantation, resulting in progressive disease, graft failure, and death. Patients with signs of active HBV replication (HBeAg and/or high levels of HBV DNA) at the time of transplantation are at increased risk. Disease recurrence occurs even more quickly after repeat transplantation (Rosen H R and Martin P. Infectious Disease Clinics of North America. September 2002; 14 (3):761-786). Overall, the use of plasma-derived polyclonal antibodies is limited because these preparations have variable activity, limited availability and there are potential hazards for the transmission of infectious agents.
In contrast, monoclonal antibodies (mAbs) can be consistently produced and do not carry the infectious risks associated with plasma-derived products.
In previous studies two fully human monoclonal antibodies were developed directed against different epitopes of hepatitis B surface antigen (HBsAg) (PCT/IL97/00184 and PCT/IL97/00183). A single administration of a mixture of these antibodies into HBV chronic carrier chimpanzees resulted in immediate reduction in HBsAg levels followed by a recurrence to initial levels within a few days (Eren et al., 2000 Hepatology 32, 588-596).
A phase 1 clinical study was conducted using a mixture of these two monoclonal antibodies (termed HBV-ABXTL and now HEPEX B™). In part A of the study patients received a single intravenous (IV) infusion of antibodies while in part B patients received 4 weekly infusions. The antibody mixture was effective in reducing HBsAg and HBV DNA levels.
HEPEX B™ for IV use was initially prepared as two separate liquid formulations for each of the antibodies (17 and 19) in phosphate buffered saline (65 mM sodium phosphate, 80 mM sodium chloride, at pH 7.0). The two mabs were mixed together prior to administration in a ratio of approximately 1:1 international units.
A need exists to develop a high dosage liquid formulation of HEPEX B that would be suitable for subcutaneous as well as intra-muscular administration. The prior liquid antibody preparations have short shelf lives and may lose biological activity of the antibodies resulting from chemical and physical instabilities during the storage. Thus, there is a need for a stable liquid formulation for an anti-HBV antibody effective to prevent HBV infection.